750W seems excessive. You could save with a 500W or greater. I wouldn't get lower than that. That motherboard will lose half its sata ports to a big graphics card. Try ASRrock's or MSI's 785g series. At this point of the game I would go ddr3, but that is just my opinion.

Direct canada has the 940 on for $179, and the 955 for $189. Even if he's not over clocking they're better than a 945. Or get an x2 550, since it'll work just as well as most quad cores for gaming. and its only around $110.

Also, I have a single card 4890 and it works well for me on a 21" monitor. You can get them under $200 very easily now if you look around a bit.
I guess since your not overclocking you can save a bit of money too by not buying a heatsink.